Such an amplifier, often called differential amplifier, is currently used in the integrated circuit industry. It is notably described in the title "Analysis and Design of Analog Integrated Circuits" by Messrs. Gray and Meyer. The gain and the maximum amplitude of the output voltage of this differential amplifier are both proportional to the product of the value of the impedance of the resistive branches and the value of the current supplied by the current source, called bias current. In certain applications, particularly radio signal receiving or processing applications in which the reduction of any form of noise which may affect the processed signals is an essential priority, this amplifier has for its function to perform both an amplification of a sinusoidal input voltage and its transformation into a square-wave output voltage. Such a transformation enables to avoid that the amplification introduces an additional noise component in the output voltage, which noise component is linked with the instantaneous value of the input voltage. Nevertheless, this transformation requires to have a high gain, so that the output voltage has edges which have such a steepness that the transitions they represent are well defined with time. This may be obtained by choosing a large value for the impedance of the resistive branch. Such a solution, however, has a major drawback: the effect of it is that the value of the maximum amplitude of the output voltage is increased considerably, which may provoke the saturation of circuits intended to receive said voltage and thus considerably disturb the operation of the system integrating the amplifier, which is unacceptable.
It is an object of the present invention to remedy this drawback to a large extent by proposing an amplifier whose gain and maximum value of the amplitude of the output voltage may be controlled independently of each other.